Method for fabricating a dual-diameter electrical conductor

ABSTRACT

The present invention discloses a multi-diameter electrical conductor for use as an embedded plug in a microelectronic device. The multi-diameter electrical conductor consists of a body portion which has a first diameter, and at least one neck portion in contact with the body portion that has at least a second diameter smaller than the first diameter. In a preferred embodiment, the multi-diameter conductor is a dual-diameter conductor providing electrical communication between an electrode and an active circuit element in a semiconductor structure and comprising a lower body portion and an upper neck portion. The conductive materials used in forming the body portion and the neck portion of the contact plug can be selected from doped polysilicon, refractory metals, metal silicides, low resistivity metals, noble metals and their alloys, adhesion layers, metallic diffusion barrier layers, and oxide and nitride diffusion barrier materials. In a preferred embodiment, the body portion is formed of a first conductive material while the neck portion is formed of a second conductive material. In an alternate embodiment, the body portion and the neck portion are formed of the same conductive material. In another alternate embodiment, the contact plug further includes an additional layer of a conductive material situated between the body portion and the neck portion formed of a material different than that used in forming the body portion and the neck portion. The additional layer of conductive material has a diameter not less than the diameter of the neck portion and not more than the diameter of the body portion.

This is a divisional of copending application Ser. No. 09/037,849 filedon Mar. 10, 1998.

FIELD OF THE INVENTION

The present invention generally relates to a dual-diameter electricalconductor for use as an embedded plug in a microelectronic device, andto a method for fabricating such a conductor, and more particularlyrelates to a dual-diameter electrical conductor consisting of a lowerbody portion and an upper neck portion wherein the neck portion isfabricated with a diameter smaller than the lithographically defineddiameter of the body portion, and to a method for fabricating such anelectrical conductor by building insulating sidewall spacers to definethe neck portion of the conductor. The use of this dual-diameter pluggeometer provides a misalignment tolerance wherein the body portion ofthe plug is protected from exposure to subsequently deposited materialsand process ambients when only the neck portion of the plug iscompletely overlapped by a subsequentially deposited conductor.

BACKGROUND OF THE INVENTION

In modem microelectronic devices, dynamic random access memory (DRAM)devices have been widely used for fast and temporary data storage. InDRAM devices, small dimensions and high capacitance value per unit areaof the capacitor memory cell are desirable characteristics for achievinga high storage density. A DRAM device is termed dynamic because thecells retain information only for a limited period of time and must beread and refreshed periodically, in contrast to a static random accessmemory (SRAM) cell which does not require periodic refresh signals inorder to retain stored data.

A typical DRAM cell is formed by a field effect transistor and a storagecapacitor. When DRAM cells were first developed, large footprint planartype storage capacitors were utilized. As the dimensions of modem memorydevices continue to shrink, other capacitor designs with reduced chipreal estate usage such as the stacked capacitor became important. In astacked capacitor, the capacitor is generally formed vertically under abit line on the surface of a silicon substrate. For a given capacitorfootprint, storage capacitor area, and thus capacitance, can beincreased by increasing the capacitor height. A stacked capacitor can beformed by a layer of a dielectric material such as silicon dioxide oroxide-nitride-oxide sandwiched between two layers of doped polysilicon.

Stacked capacitors for DRAMS are also built on substrates that containembedded contact vias which are filled with a conductive plug material.The conductive plug connects a conductive element in the underlyingsubstrate to an overlying bottom or stacked electrode. The conductiveplug typically has a diameter that is equal to the minimum lithographicdimension. In the fabrication process for the stacked capacitor, a smallamount of misalignment between the conductive plug and the stackedelectrode can be tolerated. However, problems are encountered when theelectrode fails to completely cover the plug. The problems caused by themisalignment are particularly serious for capacitors incorporating noblemetal electrodes and high epsilon dielectrics. For example, the exposedplug material may oxidize during a subsequent dielectric materialdeposition process, to produce an insulating material or undesirablevolume-change-induced stresses.

Alternatively, exposed plug material may also react with thesubsequently deposited high epsilon dielectric, or produce ahigh-leakage path over the areas where the plug and high epsilondielectric are in contact. Another consideration related to misalignmenttolerance is the critical need to avoid the situation where a singleelectrode contacts two plugs. This can occur when a severe misalignmentis coupled with an etch bias sufficient to enlarge the plug dimensionsto the point that the separation between the edges of two adjacent plugsis smaller than the electrode diameter. This etch bias can be correctedby utilizing sidewall spacers inside the contact via hole.

A conventional capacitor electrode/contact plug structure is shown inFIG. 1. The microelectronic structure 10 is built on a silicon substrate12 which has an active circuit element 14 formed in its top surface 16.On the top surface 16 of the substrate 12, a dielectric material layer18 is first deposited and then a contact hole 22 is formed therein. Intothe contact hole 22, either one or two conductive materials, such asconductive material 24 and 26 shown in FIG. 1, can be deposited andetched to form the contact plug 28. In a process where a stackedcapacitor is to be formed, a layer of electrode material is thendeposited on top of the dielectric layer 18 and the contact plug 28 andthen formed into a conductive electrode 30. The conductive electrode 30is formed by a standard lithographic method which typically has aminimum lithography dimension similar to the diameter of the contactplug 28. Due to an inevitable misalignment occurring in the lithographyprocess, the electrode 30 overlaps the contact plug 28 on only about twothirds of its top surface and thus leaves about one third of its topsurface uncovered or exposed. In a subsequent dielectric depositionprocess for forming the capacitor dielectric layer wherein hightemperature is normally required, the uncovered surface area 32 of thecontact plug 28 oxidizes and may become insulating. This provides anundesirable process element for the dielectric layer forma.

As device dimensions continue to shrink in large memory arrays, thespacings between adjacent plug/stacked electrode structures becomecloser together and as a consequence, the tolerance for misalignmentbetween the plug and the stacked electrode lithography levels decreases.Reducing the required margin for misalignment tolerance (and thus theminimum required electrode diameter) would allow more space betweenelectrodes having the-same center-to-center spacing. The extra spacingachieved can be used to better accommodate the dielectric and counterelectrode layers which are subsequently deposited for the capacitor thatmust fit between adjacent electrodes. Alternatively, reducing theminimum required electrode diameter would allow smaller footprintcapacitors with the smaller center-to-center spacing expected to benecessary for the reduced wiring dimensions and cell sizes in largerthan 4 gigabit DRAM. One way to achieve a reduced minimum electrodediameter is to utilize sidewall spacers inside a contact via hole.

Insulating sidewall spacers have been used in semiconductor structures,however, they are typically formed on the outer surfaces of structures,e.g., as sidewall coatings on gates in MOS devices for preventingshorting between silicon or silicided source and drain regions. Sidewallspacer coatings that are formed on the inside cavities have also beenreported by others. For instance, U.S. Pat. No. 5,442,213 discloses asemiconductor device that has a high dielectric capacitor with sidewallspacers. A cavity embedded in a layer of a first dielectric material isinitially provided with dielectric sidewalls and a conductive base.Sidewall spacers of a second dielectric material are then deposited toline the cavity's original dielectric sidewalls. The spacers depositedare tapered such that they are thicker at the bottom and thinner at thetop of the cavity. The objective for the sidewall spacers is to make iteasier for the barrier and bottom electrode layers of the capacitor tobe deposited on the substrate without leaving voids in the cavity.

U.S. Pat. No. 5,252,517 also discloses a method for isolating aconductive contact plug in a cavity from conductive elements that areembedded in the dielectric sidewalls of the cavity by lining the cavitywith insulating sidewall spacers. The problem of misalignment toleranceis discussed in U.S. Pat. No. 5,471,094 which discloses a self-alignedvia structure in which conductive plugs are embedded in a dielectriclayer overlying a blanket metal layer M1. The M1 metal layer is thenpatterned by etching through the dielectric/M1 stack to produce acompound plug structure including the original plug material (in areaswhere the misaligned M1 via pattern mask overlapped with the originalplug) and the dielectric material (in areas where the misaligned M1 viapattern mask overlapped with the dielectric material). However, none ofthese patents address the improvement of contact plugs by utilization ofa dual diameter geometry wherein the misalignment-intolerant featuresmay be reduced to sub-minimum lithography dimensions.

It is therefore an object of the present invention to produce amulti-diameter electrical conductor in a microelectronic structure thatdoes not have the drawbacks and shortcomings of the conventionalconductors fabricated in microelectronic structures.

It is another object of the present invention to provide amulti-diameter electrical conductor in a microelectronic structure thatconsists of a body portion that has a larger diameter and at least oneneck portion that has a smaller diameter.

It is a further object of the present invention to provide amulti-diameter electrical conductor for use in a microelectronicstructure that has a neck portion of the conductor formed in sub-minimumlithography dimensions defined by sidewall spacers.

It is another further object of the present invention to provide amethod for forming a dual-diameter electrical conductor for use in amicroelectronic structure that consists of a body portion that has alarger diameter and a neck portion that has a smaller diameter.

It is still another object of the present invention to provide adual-diameter electrical conductor for use in a microelectronicstructure which consists of a body portion that has a larger diameterformed integral with and substantially overlapping a neck portion thathas a smaller diameter.

It is yet another object of the present invention to provide adual-diameter electrical conductor for use in a microelectronicstructure for connecting stacked capacitor electrodes and underlyingcircuit elements in semiconductor devices.

It is still another further object of the present invention to provide amethod for forming a dual-diameter electrical conductor in asemiconductor device by first forming a body portion that has a largerdiameter and then forming sidewall spacers in a contact hole such that aneck portion of a smaller diameter can be formed.

It is yet another further object of the present invention to provide amethod for forming a dual-diameter electrical conductor for use in asemiconductor device by forming a body portion that has a largerdiameter with a first conductive material unitarily with a neck portionthat has a smaller diameter formed of a second conductive material thatis substantially the same or different as the first conductive material.

SUMMARY OF THE INVENTION

In accordance with the present invention, a dual-diameter electricalconductor for use in a microelectronic structure and a method for itsfabrication are provided.

In a preferred embodiment, a multi-diameter electrical conductor isprovided which includes a body portion that has a first diameter, and atleast one neck portion in contact with the body portion that has atleast a second diameter smaller than the first diameter. The conductormay be fabricated with the body portion formed of a first conductivematerial and the at least one neck portion formed of a second conductivematerial. The electrical conductor may further be provided with anadditional layer of a conductive material sandwiched between the bodyportion and the at least one neck portion, wherein the additional layerof conductive material is formed of a material different than that usedin forming the body portion and the at least one neck portion. Theadditional layer of conductive material may have a diameter not lessthan the diameter of the neck portion and not more than the diameter ofthe body portion. The conductive material used in forming the bodyportion and the neck portion can be at least one member selected fromdoped polysilicon, refractory metals, metal silicides, low resistivitymetals, noble metals and their alloys, metallic diffusion barriermaterials, and oxide and nitride diffusion barrier materials. The lowresistivity metals include Al, Al—Cu, Cu and Cu alloys, the metallicdiffusion barrier materials include refractory metals, while the oxide,nitride and suicide diffusion barrier materials include TiN, TaSiN,TiAlN, WN, TaN and WSi. The electrical conductor formed can beadvantageously used in a semiconductor device to provide electricalcommunication between an overlying electrode and an underlying circuitelement. By utilizing the present invention novel method, the firstdiameter of the body portion can be substantially equal to a minimumlithographic dimension, while the second diameter of the neck portioncan be less than the minimum lithographic dimension.

In another preferred embodiment, a dual-diameter electrical conductor isprovided which includes a body portion that has a first diameter, and aneck portion in contact with the body portion that has a second diametersmaller than the first diameter. The body portion of the dual-diameterconductor substantially or completely overlaps the neck portion. Theelectrical conductor provides electrical communication between anelectrode and a circuit element in a semiconductor device.

In another preferred embodiment, a microelectronic device that isfabricated with a dual-diameter electrical conductor therein isprovided. The dual-diameter electrical conductor is constructed by abody portion that has a first diameter, and a neck portion in contactwith the body portion that has a second diameter smaller than the firstdiameter.

In still another preferred embodiment, a dynamic random access memorydevice that is fabricated with a dual-diameter electrical conductortherein is provided. The dual-diameter electrical conductor in the DRAMdevice is constructed with a body portion that has a first diameter, anda neck portion in contact with the body portion that has a seconddiameter smaller than the first diameter. The memory device has at leastone of its capacitor electrodes in electrical communication with theneck portion of the dual-diameter electrical conductor.

The present invention is further directed to a method for fabricating adual-diameter electrical conductor that can be carried out by theoperating steps of first providing a substrate that has a firstconductive region, then depositing a layer of a first dielectricmaterial on the substrate, then etching a first opening in the firstdielectric material layer to expose the first conductive region in thesubstrate, then depositing a second conductive material into the firstopening in the first dielectric material layer to form a body portion ofthe conductor, then removing a surface layer of the second conductivematerial to at least partially expose an upper sidewall surface in thefirst opening, then forming sidewall spacers of a second dielectricmaterial on the upper sidewall surface of the first opening therebydefining a second opening through which the body portion of theconductor is exposed, and depositing a third conductive material intothe second opening and forming a neck portion of the conductor that isin contact with the body portion of the conductor. The first opening inthe first dielectric material layer can be advantageously formed by areactive ion etching method. The first opening formed can be a contacthole that at least partially exposes the first conductive region in thesubstrate. The method may further include the steps of depositing andforming a stacked capacitor electrode on top of and in electricalcommunication with the neck portion of the electrical conductor. Thesidewall spacers of the second dielectric material can be advantageouslyformed by a conformal deposition technique followed by an anisotropicetching process. The second opening defined by the sidewall spacersformed in the first opening is smaller than the first opening, thusallowing the formation of a neck portion of the electrical conductorhaving a diameter smaller than that of the body portion of theconductor.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionand the appended drawings in which:

FIG. 1 is an enlarged, cross-sectional view of a conventionalmicroelectronic structure showing a stacked capacitor electrode onlypartially overlapping a contact plug formed in a dielectric layer.

FIG. 2 is an enlarged, cross-sectional view of a present inventionpreferred embodiment showing a reduced-dimension neck portion of thecontact plug being completely overlapped by a misaligned stackedelectrode.

FIG. 3A is an enlarged, cross-sectional view of the present inventionpreferred embodiment showing a reduced-dimension neck portion of thecontact plug being completely overlapped by an aligned stackedelectrode.

FIG. 3B is an enlarged, cross-sectional view of an alternate embodimentof the present invention novel structure.

FIG. 3C is an enlarged, cross-sectional view of a second alternateembodiment of the present invention novel structure incorporating theuse of an additional conductive material layer.

FIG. 3D is an enlarged, cross-sectional view of a third alternateembodiment of the present invention novel structure incorporating theuse of an additional conductive material layer.

FIG. 4 is an enlarged, cross-sectional view of the present inventionpreferred embodiment contact plug structure with completed stackedcapacitors formed on top.

FIG. 5A is an enlarged, cross-sectional view of a substrate and adielectric layer for forming the present invention preferred embodimentstructure.

FIG. 5B is an enlarged, cross-sectional view of the present inventionpreferred embodiment structure of FIG. 5A having a contact hole formedon top of the circuit element in the substrate.

FIG. 5C is an enlarged, cross-sectional view of the present inventionpreferred embodiment contact plug structure of FIG. 5B having aconductive material filling the contact hole.

FIG. 5D is an enlarged, cross-sectional view of the present inventionpreferred embodiment contact plug structure of FIG. 5C having thecontact plug formed.

FIG. 5E is an enlarged, cross-sectional view of the present inventionpreferred embodiment contact plug structure of FIG. 5D having a toplayer of the contact plug removed by a selective etching process.

FIG. 5F is an enlarged, cross-sectional view of the present inventionpreferred embodiment contact plug of FIG. 5E having a second dielectricmaterial deposited into the contact hole.

FIG. 5G is an enlarged, cross-sectional view of the present inventionpreferred embodiment contact plug structure of FIG. 5F having sidewallspacers formed inside the contact hole.

FIG. 5H is an enlarged, cross-sectional view of the present inventionpreferred embodiment contact plug structure of FIG. 5G having a secondconductive material deposited into the opening formed by the sidewallspacers forming a neck portion of the plug.

FIG. 5I is an enlarged, cross-sectional view of the present inventionpreferred embodiment contact plug structure of FIG. 5H having acapacitor electrode formed on top of the neck portion of the contactplug.

FIG. 6A is an enlarged, cross-sectional view of the present inventionalternate embodiment contact plug having a second conductive layerdeposited into an opening formed by the sidewall spacers.

FIG. 6B is an enlarged, cross-sectional view of the present inventionalternate embodiment contact plug structure of FIG. 6A having thecapacitor electrode formed in contact with the neck portion of thecontact plug.

FIG. 7A is an enlarged, cross-sectional view of the present inventionsecond alternate embodiment contact plug structure showing a bodyportion of a contact plug is formed.

FIG. 7B is an enlarged, cross-sectional view of the present inventionsecond alternate embodiment contact plug of FIG. 7A having an additionalconductive material layer deposited on top filing the recess.

FIG. 7C is an enlarged, cross-sectional view of the present inventionsecond alternate embodiment of FIG. 7B having the additional conductivematerial layer planarized.

FIG. 7D is an enlarged, cross-sectional view of the present inventionsecond alternate embodiment of FIG. 7C having the additional conductivematerial layer formed by a selective etching process.

FIG. 7E is an enlarged, cross-sectional view of the present inventionsecond alternate embodiment of FIG. 7D having a second dielectricmaterial deposited into the recess in the contact hole.

FIG. 7F is an enlarged, cross-sectional view of the present inventionsecond alternate embodiment of FIG. 7E having the sidewall spacersformed from the second dielectric material.

FIG. 7G is an enlarged, cross-sectional view of the present inventionsecond alternate embodiment contact plug structure of FIG. 7F having asecond conductive material layer deposited into the recess formed by thesidewall spacers.

FIG. 7H is an enlarged, cross-sectional view of the present inventionsecond alternate embodiment contact plug structure of FIG. 7G having thecapacitor electrode formed in contact withly with the neck portion ofthe contact plug.

DETAILED DESCRIPTION OF THE PREFERRED AND ALTERNATE EMBODIMENTS

The present invention provides a multi-diameter electrical conductor foruse in a microelectronic structure and a method for forming suchconductor. The conductor can be formed with either a body portion and aneck portion, or can be formed with a body portion and two or more neckportions by additional processing steps. In a most likely embodiment, adual-diameter electrical conductor is formed by a body portion that hasa larger diameter and a neck portion that has a smaller diameter.

Referring initially to FIG. 2, wherein a present inventionmicroelectronic structure 40 is shown. The microelectronic structure 40consists of a semi-conducting substrate 12 having an active circuitelement 14 formed in a top surface 16. Into a first dielectric materiallayer 18, such as a layer formed of SiO₂, a contact hole 42 is formed bya reactive ion etching process, and then filled with a first conductivematerial 44 and a second conductive material 46 forming the contact plug48. The formation of the body portion 44 by the first conductivematerial and the formation of the neck portion 46 by the secondconductive material shall be described in detail in a later section. Astacked electrode 52 for a stacked capacitor (not shown) is then formedto completely overlap the top of the neck portion 46 of the contact plug48. When compared to a conventional structure shown in FIG. 1, theadvantages of the present invention become apparent in that when thesame size capacitor electrode is formed on top of the contact plug, theoff-set of the electrode due to misalignment does not prevent theelectrode from completely overlapping the contact plug in the presentinvention novel structure.

The present invention relates to the geometry of conductive plug or viastructures that are used for electrically connecting conductive elementsin microelectronic devices such as high density DRAM's where, forexample, the conductive elements to be connected may include the stackedcapacitor electrodes and the underlying circuit elements. In particular,the present invention relates to structures and fabrication techniquesfor a class of misalignment-tolerant contact plugs that have adual-diameter geometry in which plug surfaces contactingmisalignment-intolerant features may be reduced to sub-minimumlithography dimensions by means of sidewall spacers.

The dual-diameter contact plug structure of the present invention isembedded in a dielectric layer. The contact plug has a lower or bodyportion that has a lithographically designed diameter, and an upper orneck portion that has a diameter smaller than the lithographicallydefined diameter of the body portion. In a preferred embodiment, bodyportion diameter matches the minimum lithography dimension, while theneck portion diameter has a sub-minimum lithography dimension. The neckportion of the contact plug is fabricated by first coating insulatingsidewall spacers on the upper portion of the dielectric cavity in whichthe contact plug body portion is formed, and then filling an openingformed by the sidewall spacers with a conductive material.

FIGS. 3A^(˜) 3D illustrate four of the many possible embodiments of thepresent invention. FIG. 3A illustrates a preferred embodiment of thepresent invention microelectronic structure 50. The microelectronicstructure 50 consists of a semi-conducting substrate 12, and an activecircuit element 14 formed in a top surface 16 of the substrate. In afirst dielectric material layer 18, a contact hole 54 is formed and thensubsequently filled with a first conductive material forming a bodyportion 56 and a second conductive material forming a neck portion 58for the contact plug 60. A conductive electrode 62 is then deposited andformed on top of the microelectronic structure 50. As shown in FIG. 3A,the conductive material used to form the neck portion 58 and theconductive material used to form the electrode 62 are different. Thedetails for formation of this preferred embodiment structure is givenbelow in Example 1.

FIG. 3B illustrates an alternate embodiment of the present inventionmicroelectronic structure 70. In this alternate embodiment, on top of abody portion 64, a neck portion 66 and a capacitor electrode 68 areformed by the same conductive material in a single deposition andforming process. The details for formation of this embodiment is givenbelow in Example 2.

FIG. 3C illustrates a second alternate embodiment of the presentinvention contact plug in a microelectronic structure 80. It is seenthat on top of a body portion 72 of the contact plug 84, an additionalconductive material layer 74 is first deposited and formed prior to thedeposition and forming of the neck portion 76 and the capacitorelectrode 78. A contact plug 84 is thus formed with the additional layerof conductive material 74 sandwiched between the neck portion 76 and thebody portion 72. Detail processing steps for forming the secondalternate embodiment contact plug are shown below in Example 3.

FIG. 3D illustrates a third alternate embodiment of the presentinvention contact plug in a microelectronic structure 85. Note that theembodiments of FIGS. 3C and 3D differ by the fact that in FIG. 3C theadditional conductive layer 74 is below the neck portion 76 of contactplus the material for the neck portion 176 of contact plug 184 and isintegral with capacitor electrode 178.

The materials used in forming the neck portions 58 and 176 and theadditional conductive layer 74 are preferably barriers to plug materialdiffusion, electrode material diffusion and/or oxygen diffusion. Itshould be noted that in FIGS. 3A^(˜) 3D, the active circuit element 14and the stacked electrodes 62, 68, 78, 178 and are merely given asexamples of two conductive elements which may be electrically connectedby the present invention novel contact plug. The present invention novelcontact plug can be utilized equally well in providing electricalcommunications between any other two conductive elements than thoseshown in the various embodiments.

The conductive materials utilized in forming the neck portion and thebody portion of the contact plug may be the same or may be different.The materials are typically selected from the groups of conductivematerials which include doped polysilicon, refractory metals such astungsten, silicides, low resistivity metals such as Al, Al—Cu, Cu, Cualloys, noble metals and their alloys, metallic diffusion barriermaterials such as Ta and W, and oxide and nitride diffusion barriermaterials such as TiN, TaSiN, TiAlN, WN, TaN and WSi, adhesion layerssuch as Ti, and alloys or mixtures of these materials, alone or inlayered combinations. Each of the three embodiments shown in FIGS.3A^(˜) 3D has its own advantages and disadvantages. For example, thepreferred embodiment of FIG. 3A has the advantage of simplicity, but mayfail if the materials of the capacitor electrode 62 and the body portion56 interdiffuse during processing. However, all four embodiments of thedual-diameter contact plugs have the diameter of the plug body portionequal to the minimum lithography dimension and the diameter of the plugneck portion smaller than the minimum lithography dimension.

FIG. 4 illustrates a microelectronic structure 90 which has twocompleted capacitor structures 86 and 88 incorporating the dual-diametercontact plug structure illustrated in the preferred embodiment of thepresent invention (shown in FIG. 3A). The capacitors of FIG. 4 contain aconformally deposited layer 92 of a ferroelectric or capacitordielectric layer on the bottom (or stacked) electrodes 62, and acounterelectrode (or plate electrode) 94. The bottom electrodes 62 areelectrically connected to conductive substrate regions 14 by means ofplug body portions 56 and plug neck portions 58.

EXAMPLE 1

Example 1 illustrates the processing steps for forming the presentinvention preferred embodiment contact plug of FIG. 3A in FIGS. 5A-5I.FIG. 5A is an enlarged, cross-sectional view of an electronic structure50 having a first dielectric material layer 18 deposited on a topsurface 16 of a semi-conducting substrate 12 covering the conductivesubstrate region 14. A typical dielectric material used is SiO₂. Acontact via hole 54 is then etched by a reaction ion etching techniquein the first dielectric material layer 18 as shown in FIG. 5B. Thecontact via hole 54 is then overfilled with a conductive plug material102 as shown in FIG. 5C. The conductive plug material layer 102 can beplanarized by a process such as chemical mechanical polishing (CMP) forforming a contact plug 104. This is shown in FIG. 5D. The plug structureis then recessed, as shown in FIG. 5E, by a selective etching techniquesuch as reactive ion etching by utilizing an etch chemistry that has alarge etch selectivity ratio between a dielectric layer of SiO₂ and aconductive material layer of doped polysilicon. An etch process by usingSF₆ or other fluorine-based gases is capable of producing an etchselectivity ratio of about 50:1 between doped polysilicon and SiO₂. Anyother etch gas that is capable of producing an etch rate ratio of morethan 5:1 can be suitably used in the present invention novel method forforming the contact plugs. In the next step of the process, a layer of asecond dielectric material 108 is conformally deposited on top of theelectronic structure 50, as shown in FIG. 5F. The second dielectricmaterial layer 108 is then anisotropically etched in a reactive ionetching process to form sidewall spacers 110. This is shown in FIG. 5G.A third conductive material is then deposited into opening 112 formed bythe sidewall spacers 110 to form a neck portion 114 of the contact plug60. This is shown in FIG. 5H. The neck portion 113 can be formed after adeposition process and a planarization process are conducted on thethird conductive material. In a final step of the process, an electrodematerial 116 is deposited and patterned to produce the structure shownin FIG. 5I.

EXAMPLE 2

An alternate embodiment of the present invention contact plug is shownin FIGS. 6A and 6B in enlarged, cross-sectional views. The structure 70produced is similar to that previously shown in FIG. 3B. The formationof the alternate embodiment of the present invention contact plug isillustrated starting from a structure similar to that shown in FIG. 5G.Into an opening 112 formed by sidewall spacers 110, a layer of electrodematerial 120 is deposited on top of the microelectronic structure 70.The electrode layer 120 is patterned to then form the capacitorelectrode 68 as shown in FIG. 6B. The neck portion 66 of the contactplug 82 corresponds to the part of the electrode material 120 that alsofunctions as the plug neck portion.

EXAMPLE 3

A second alternate embodiment of the present invention novel contactplug of FIG. 3C and one method of its formation process are shown inFIGS. 7A˜7H. For instance, FIG. 7A is an enlarged, cross-sectional viewof a microelectronic structure 80 in a similar processing state as thatshown in FIG. 5E. A plug body portion 72 is first formed and recessed bya selective etch process forming an opening 122. A conductive (orconductive barrier) material layer 124 is then deposited on top of themicroelectronic structure 80 as shown in FIG. 7B. The conductivematerial layer 124 is then planarized by a process such as a chemicalmechanical polishing method forming a conductive plug body cap 126 ontop of the body portion 72 for the contact plug. This is shown in FIG.7C. The conductive plug body cap 126 is then recessed in a selectiveetching process to form an opening 128 with exposed sidewall surface130. On top of the exposed sidewall surface 130, sidewall spacers 134are formed by first depositing a dielectric layer 132 into opening 128on top of the microelectronic structure 80. These steps are shown inFIGS. 7D, 7E and 7F. A layer of an electrode material 142 is thendeposited into opening 138 and on top of the microelectronic structure80, as shown in FIG. 7G. After the electrode material layer 142 ispatterned, a capacitor electrode 78 is formed for as providingelectrical communication with the neck portion 76, the conductive region126 and the body portion 72 of the contact plug 84. Similar to theembodiment shown in FIG. 6B, the electrode portion 76 corresponds to thepart of the electrode material 142 that doubles as the plug neckportion.

An alternate route from the structure of FIG. 7A to the structure ofFIG. 7D might comprise the step of directly forming conductive plug cap126 by a process such as selective chemical vapor deposition.Self-aligned silicide formation may also be used to form the plug bodycap layer 126 if plug body cap layer 126 is a metal silicide and plugbody material is silicon or silicon-contributing. Self-aligned silicideformation would comprise the steps of depositing a metal layer on thestructure of FIG. 7A, heating in such a manner as to locally cause themetal over the plug to form a metal silicide, and then selectivelyetching unreacted metal remaining over the non-plug regions of thesubstrate.

The present invention has therefore been amply demonstrated in threedifferent embodiments shown in FIGS. 2^(˜) 7H. The present inventionprovides a novel structure and a novel fabrication method for a class ofmisalignment-tolerant contact plugs that have a dual-diameter geometry.The plug surfaces which contact misalignment-intolerant features may bereduced to sub-minimum lithography dimensions by means of sidewallspacers. By utilizing the dual-diameter plug geometry, it is possiblefor the plug to have the minimum lithography diameter over most of itslength, but a sub-minimum lithography dimensions on its critical contactsurfaces. Such a plug could be suitably used, for example, to connectconductive device elements in a substrate to a DRAM stacked electrodewhose diameter would not have to be any wider than the minimumlithography dimension used for the widest portion of the contact plug.

The novel conductive plug structure of the present invention istypically surrounded on its sides by a dielectric material. The lower(or body) portion of the plug has a lithographically designed diameter,and is surrounded and contacted on its sides by a first dielectricmaterial. The lower body portion would typically be formed by forming acavity in a layer of first dielectric material and then partiallyfilling the cavity with a plug body material. The upper (or neck)portion of the plug has a diameter smaller than the lithographicallydesigned diameter of the plug body, and is surrounded and contacted onits sides by a second dielectric material. The neck portion of the plugstructure is provided by coating insulating sidewall spacers of thesecond dielectric material on the unfilled portion of the cavity in thefirst dielectric in which the plug body is situated, and then fillingthe opening formed by the sidewall spacers with the conductive materialof the plug neck portion.

The first and second dielectric materials may be the same or different,and would typically be selected from the groups of insulating oxides andnitrides such as SiO₂ and silicon nitride. The first dielectric may alsocomprise one or more layers of two or more different dielectrics, suchas a layer of silicon nitride sandwiched between upper and lower layersof SiO₂.

The narrow diameter section of the contact plug has been called the neckportion of the plug, while the wider portion of the plug has been calledthe body portion of the plug. The neck portion of the plug may also beviewed as a plug extension. The neck porterial, or from a mixture,alloy, of two or more materials, or layered combination. In addition,the neck portion of the plug may be formed at the bottom of the plug,all along the plug or at both top and bottom portions of the plug.

While the present invention has been described in an illustrativemanner, it should be understood that the terminology used is intended tobe in a nature of words of description rather than of limitation.

Furthermore, while the present invention has been described in terms ofa preferred embodiment and two alternate embodiments, it is to beappreciated that those skilled in the art will readily apply theseteachings to other possible variations of the inventions.

The embodiment of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method for fabricatinga dual-diameter electrical conductor comprising the steps of: providinga substrate having a first conductive region formed of a firstconductive material, depositing a layer of a first dielectric materialon said substrate, etching a first opening in said first dielectricmaterial layer by reactive ion etching to expose said first conductiveregion in the substrate, depositing a second conductive material intosaid first opening in said first dielectric material layer forming abody portion of the conductor, removing a surface layer of said secondconductive material to at least partially expose an upper sidewallsurface in said first opening, forming sidewall spacers of a seconddielectric material on said upper sidewall surface of said first openingthereby defining a second opening through which said body portion of theconductor is exposed, and depositing a third conductive material intosaid second opening and forming a neck portion of the conductor that isin contact with the body portion of said conductor, said neck portionhaving a diameter at a top surface of the neck portion smaller than adiameter of said body portion.
 2. A method for fabricating adual-diameter electrical conductor according to claim 1, wherein saidfirst opening formed in said first dielectric material layer is acontact hole that at least partially exposes said first conductiveregion in said substrate.
 3. A method for fabricating a dual-diameterelectrical conductor according to claim 1 further comprising the stepsof depositing and forming a stacked capacitor electrode on top of and inelectrical communication with the neck portion of said electricalconductor.
 4. A method for fabricating a dual-diameter electricalconductor according to claim 1, wherein said surface of the secondconductive material layer being etched away to a level below the topsurface of said first opening such that an upper sidewall surface in thefirst opening is re-exposed.
 5. A method for fabricating a dual-diameterelectrical conductor according to claim 1, wherein said sidewall spacersof a second dielectric material are formed by a conformal depositiontechnique followed by an anisotropic etching process.
 6. A method forfabricating a dual-diameter electrical conductor according to claim 1,wherein said second opening defined by said sidewall spacers formed insaid first opening being smaller than said first opening and thusallowing the formation of a neck portion of the electrical conductorsmaller than the body portion of the conductor.
 7. A method forfabricating a dual-diameter electrical conductor comprising the stepsof: providing a substrate having a first conductive region formed or afirst conductive material, depositing a layer of a first dielectricmaterial on said substrate, etching a first opening in said firstdielectric material layer to expose said first conductive region in thesubstrate, depositing a second conductive material into said firstopening in said first dielectric material layer forming a body portionof the conductor, removing a surface layer of said second conductivematerial to at least partially expose an upper sidewall surface in saidfirst opening, forming sidewall spacers of a second dielectric materialon said upper sidewall surface of said first opening thereby defining asecond opening through which said body portion of the conductor isexposed, depositing a third conductive material into said second openingand forming a neck portion of the conductor that is in contact with thebody portion of said conductor, said neck portion having a diameter at atop surface of the neck portion smaller than a diameter of said bodyportion, and depositing and forming a stacked capacitor electrode on topof and in electrical communication with said neck portion of saidelectrical conductor.
 8. A method for fabricating a dual-diameterelectrical conductor according to claim 7, wherein said first opening insaid first dielectric material layer is formed by a reactive ion etchingmethod.
 9. A method for fabricating a dual-diameter electrical conductoraccording to claim 7, wherein said first opening formed in said firstdielectric material layer is a contact hole that at least partiallyexposes said first conductive region in said substrate.
 10. A method forfabricating a dual-diameter electrical conductor according to claim 7,wherein said surface of the second conductive material layer beingetched away to a level below the top surface of said first opening suchthat an upper sidewall surface in the first opening is re-exposed.
 11. Amethod for fabricating a dual-diameter electrical conductor according toclaim 7, wherein said sidewall spacers of a second dielectric materialare formed by a conformal deposition technique followed by ananisotropic etching process.
 12. A method for fabricating adual-diameter electrical conductor according to claim 7, wherein saidsecond opening defined by said sidewall spacers formed in said firstopening being smaller than said first opening and thus, allowing theformation of a neck portion of the electrical conductor smaller than thebody portion of the conductor.